Chromatography Forum

This is my company's calculation for potency determination. Most of the variables are %w/w except for HPLC purity and enantiomeric excess. Obviously since everyone agrees with it, I'm the one in error, but I can't understand how this can be correct. Reason one is that we're comparing apples and oranges with %w/w parameters and area% ones. Reason 2. How can area% be in the calculation unless we assume relative response factors are all 1? I have to be missing something which is why I post this. What is it?

Potency, % = [100.00% - (Chloride,% x 1.0285) - (H₂O,%) - (ROI,%) - (Res Sol,%) - (HM, %)] x [(HPLC Purity, % - Enan Cont, %)/100]

How can area% be in the calculation unless we assume relative response factors are all 1?

That's exactly what *is* assumed. It's not ideal, but if you don't have access to pure standards of all the compounds, you have no choice. An alternative is to use one of the evaporative detectors (ELSD or CAD) where response factors actually *are* approximately equal. A drawback to *that* is a limited (or nonexistant) linear range.